Ceramics such as zirconia ZrO2 or alumina Al2O3 are widely employed in horology for making scratchproof cases, watchbands or bracelets. The colour of pure zirconia or pure alumina is a milky white which has few applications in horology.
Methods for colouring zirconia are already widely used by ceramic manufacturers. They generally consist in introducing a pigment or an oxide in a powder state into the zirconium oxide based mixture, prior to an injection moulding step. However, this type of method does not allow designs to be made on ceramic part, since the latter are coloured throughout.
Moreover, a local colouring method for zirconium oxide is disclosed in EP Patent No 0 741 117. This method consists in illuminating the surface of a zirconium oxide part, for a sufficiently long time to obtain a change in colour from milky white to black. It enables an image to be formed, but the contrast obtained, black on milky white, is very strong and unattractive.